Bacterial abundance in relation to surface area and organic content of marine sediments

Based on direct measurements on surface sediments collected from an intertidal salt marsh, a positive relationship was demonstrated between bacterial abundance and specific surface area of sediment. While this relationship has been postulated previously, this is the first direct confirmation that it holds over a wide range of sediment types. A laboratory experiment was conducted to determine the effects of specific surface area, distribution of surface area, and organic loading on bacterial colonization. Model sediments included angular silica particles, kaolin, and spherical glass beads, used singly or in mixtures. Organic loading resulted in substantial enhancement of bacterial colonization. Distribution of surface area controlled by textural, shape, and sorting, had a complex effect, with glass bead sediments generally supporting better colonization than silica particles or kaolin. The effect of specific surface area was noted only in restricted comparisons of similarly shaped glass beads.     

Determination of the abundance of viable tintinnid cysts in marine sediments in Hiroshima Bay, the Seto Inland Sea of Japan, using a modified MPN method

A modified MPN method was developed for enumerating viable tintinnidcysts in marine sediments Using this MPN method the abundanceof tintinnid cysts was estimated in Hiroshima Bay, the SetoInland Sea of Japan.     

Short-term changes of meiofaunal abundance in intertidal sediments

Some species of various meiofaunal taxa may actively emerge from the sediment and swim in the water column, preferably at night. In the water column they get dispersed by tital currents. The hypothesis that this drift may cause significant short-term changes in the abundance of these species was tested. Such changes were verified for harpacticoid copepods and plathelminths. Depending on the hydrographic conditions, abundance changes may be unpredictable or show regularly alternating patterns. In the light of these results, small-scale spatial estimates of abundance become generally very difficult to make in the taxa containing emergent species. It is suggested that reliable averages can only be obtained by repeated or large-scale spatial sampling.     

Significance of monosulcate pollen abundance in Mesozoic sediments

Monosulcate pollen was produced by at least six plant orders in the Mesozoic. Megafossils of these orders are abundant in many Mesozoic sediments, but dispersed monosulcate pollen grains are commonly less than 10% of total sporomorphs (spores and pollen) in a sample. This paper presents possible explanations for the different relative frequencies of megafossils and pollen grains of monosulcate-producing plants (some of the explanations apply to only a few taxa): fragility of the pollen exines, destruction of the pollen on the plant by insects, poor pollen dispersal because of zoophily and small plant size, and, probably most importantly, overrepresentation of the plants by their generally deciduous leaves. Mesozoic monosulcate pollen was different in several ways from pollen of modern gymnosperms; furthermore, monosulcate-producing plants were not as abundant in the Mesozoic vegetation as has been generally thought.     

Prokaryotic diversity in Zostera noltii-colonized marine sediments

The diversity of microorganisms present in a sediment colonized by the phanerogam Zostera noltii has been analyzed. Microbial DNA was extracted and used for constructing two 16S rDNA clone libraries for Bacteria and Archaea. Bacterial diversity was very high in these samples, since 57 different sequences were found among the 60 clones analyzed. Eight major lineages of the Domain Bacteria were represented in the library. The most frequently retrieved bacterial group (36% of the clones) was delta-Proteobacteria related to sulfate-reducing bacteria. The second most abundant group (27%) was gamma-Proteobacteria, including five clones closely related to S-oxidizing endosymbionts. The archaeal clone library included members of Crenarchaeota and Euryarchaeota, with nine different sequences among the 15 analyzed clones, indicating less diversity when compared to the Bacteria organisms. None of these sequences was closely related to cultured Archaea organisms.     

Bacterial diversity in marine hydrocarbon seep sediments

Marine seeps introduce significant amounts of hydrocarbons into oceans and create unusual habitats for microfauna and -flora. In the vicinity of chronic seeps, microbes likely exert control on carbon quality entering the marine food chain and, in turn, hydrocarbons could influence microbial community composition and diversity. To determine the effects of seep oil on marine sediment bacterial communities, we collected sediment piston cores within an active marine hydrocarbon seep zone in the Coal Oil Point Seep Field, at a depth of 22 m in the Santa Barbara Channel, California. Cores were taken adjacent to an active seep vent in a hydrocarbon volcano, on the edge of the volcano, and at the periphery of the area of active seepage. Bacterial community profiles were determined by terminal restriction fragment length polymorphisms (TRFLPs) of 16S ribosomal genes that were polymerase chain reaction (PCR)-amplified with eubacterial primers. Sediment carbon content and C/N ratio increased with oil content. Terminal restriction fragment length polymorphisms suggested that bacterial communities varied both with depth into sediments and with oil concentration. Whereas the apparent abundance of several peaks correlated positively with hydrocarbon content, overall bacterial diversity and richness decreased with increasing sediment hydrocarbon content. Sequence analysis of a clone library generated from sediments collected at the periphery of the seep suggested that oil-sensitive species belong to the gamma Proteobacteria and Holophaga groups. These sequences were closely related to sequences previously recovered from uncontaminated marine sediments. Our results suggest that seep hydrocarbons exert a strong selective pressure on bacterial communities in marine sediments. This selective pressure could, in turn, control the effects of oil on other biota in the vicinity of marine hydrocarbon seeps.     

High abundance of virulence gene homologues in marine bacteria

Marine bacteria can cause harm to single-celled and multicellular eukaryotes. However, relatively little is known about the underlying genetic basis for marine bacterial interactions with higher organisms. We examined whole-genome sequences from a large number of marine bacteria for the prevalence of homologues to virulence genes and pathogenicity islands known from bacteria that are pathogenic to terrestrial animals and plants. As many as 60 out of 119 genomes of marine bacteria, with no known association to infectious disease, harboured genes of virulence-associated types III, IV, V and VI protein secretion systems. Type III secretion was relatively uncommon, while type IV was widespread among alphaproteobacteria (particularly among roseobacters) and type VI was primarily found among gammaproteobacteria. Other examples included homologues of the Yersinia murine toxin and a phage-related 'antifeeding' island. Analysis of the Global Ocean Sampling metagenomic data indicated that virulence genes were present in up to 8% of the planktonic bacteria, with highest values in productive waters. From a marine ecology perspective, expression of these widely distributed genes would indicate that some bacteria infect or even consume live cells, that is, generate a previously unrecognized flow of organic matter and nutrients directly from eukaryotes to bacteria.     

Distribution of actinomycetes in near-shore tropical marine sediments

Actinomycetes were isolated from near-shore marine sediments collected at 15 island locations throughout the Bahamas. A total of 289 actinomycete colonies were observed, and all but 6 could be assigned to the suprageneric groups actinoplanetes and streptomycetes. A bimodal distribution in the actinomycete population in relation to depth was recorded, with the maximum numbers occurring in the shallow and deep sampling sites. This distribution can be accounted for by a rapid decrease in streptomycetes and an increase in actinoplanetes with increasing depth and does not conform to the theory that actinomycetes isolated from marine sources are of terrestrial origin. Sixty-three of the isolated actinomycetes were tested for the effects of seawater on growth. Streptomycete growth in nonsaline media was reduced by 39% compared with that in seawater. The actinoplanetes had a near obligate requirement of seawater for growth, and this is presented as evidence that actinomycetes can be physiologically active in the marine environment. Problems encountered with the enumeration of actinomycetes in marine sediments are also discussed.     

The biodiversity of macrofaunal organisms in marine sediments

Marine sediments cover most of the ocean bottom, and the organisms that reside in these sediments therefore constitute the largest faunal assemblage on Earth in areal coverage. The biomass in these sediments is dominated by macrofauna, a grouping of invertebrate polychaetes, molluscs, crustaceans and other phyla based on size. Globally, only a small portion of marine habitats have been sampled for macrofauna, but sampled areas have led to global estimates of macrofaunal species number ranging from 500,000 to 10,000,000. Most of these species are undescribed, and global syntheses of patterns of individual taxa and biodiversity are few and based on limited samples. The significance of biodiversity in marine sediments to ecosystem processes is poorly understood, but individual species and functional groups are known to carry out activities that have global importance. Macrofaunal activity impacts global carbon, nitrogen and sulphur cycling, transport, burial and metabolism of pollutants, secondary production including commercial species, and transport of sediments. Documented extinctions of marine macrofauna are few, but the ramifications of species loss through habitat shrinkage and undocumented extinctions are unknown. Limited data suggest there is substantial functional redundancy in macrofauna within trophic groups but whether this redundancy is sufficient to allow species loss without significantly altering ecosystem processes is unknown. Sorely needed are experiments that test specific hypotheses on biodiversity, redundancy, and ecosystem processes as they relate to marine macrofauna.     

Higher abundance of bacteria than of viruses in deep Mediterranean sediments

The interactions between viral abundance and bacterial density, biomass, and production were investigated along a longitudinal transect consisting of nine deep-sea stations encompassing the entire Mediterranean basin. The numbers of viruses were very low (range, 3.6 x 10(7) to 12.0 x 10(7) viruses g(-1)) and decreased eastward. The virus-to-bacterium ratio was always < 1.0, indicating that the deep-sea sediments of the Mediterranean Sea are the first example of a marine ecosystem not numerically dominated by viruses. The lowest virus numbers were found where the lowest bacterial metabolism and turnover rates and the largest cell size were observed, suggesting that bacterial doubling time might play an important role in benthic virus development.     

Dynamics of virus abundance in coastal seawater

Abstract: The short term dynamics of virus abundance in coastal sea water was investigated by frequent sampling of open ecosystems and of water incubated in bottles in situ. Sampling intervals were 6–10 min. The viral abundance showed significant temporal fluctuations both in situ and in the bottles and it changed in some cases by a factor of 2–4 within 10–20 min. Laboratory incubations showed that production and release of viruses wre not induced or stimulated by nutrient addition, high light intensities or transient increase in temperatures ca. 10°C. Our interpretation of these results is that they result from synchronous lysis and release of virus particles from bacterial hosts and a rapid disintegration of these particles when released in sea water.